Hydrodynamic reversing gear

ABSTRACT

In hydrodynamic reversing gears, in order to eliminate excessive heating due to windage losses generated during rotation in the absence of hydraulic liquid, there are provided in the convertor work chamber air flow obstructing members movable into an operative (blocking) position when hydraulic liquid is withdrawn from the work chamber and movable into an inoperative (flow transmitting) position when hydraulic liquid is introduced into the work chamber.

United States Patent Muller et a1.

[54] HYDRODYNAMIC REVERSING GEAR Helmut Muller, Heidenheim; Gustav Pistl, Nattheim, both of Germany Voith Getriebe KG, Heidenheim (Brenz), Germany [22] Filed: Nov. 9, 1970 [21] Appl.No.: 87,835

[72] Inventors:

[73] Assignee:

[45] July 18,1972

Primary ExaminerEdgar W. Geoghegan Attorney-Edwin E. Greigg [57] ABSTRACT [30] Foreign Application Priority Data in hydrodynamic reversing gears, in order to eliminate excessive heating due to windage losses generated during rotation in NOV. 8, 1969 Germany ..P 19 56 244.8 the absence of hydraulic liquid there are pro ided in th convertor work chamber air flow obstructing members movable [52] US. Cl ..60/54 into an operative (blocking) position when hydraulic liquid is [51] Int. Cl withdrawn from the work chamber and movable into an in- [58] Field of Search ..60/54 operative (flow transmitting) position when hydraulic liquid is introduced into the work chamber. 7 [56] References Cited 9 Claim, 14 Drawing Figures UNITED STATES PATENTS 2,063,471 12/ 1936 Stedefeld ..60/54 X agar/.004

PATENTEB JUL] 8 m2 SHEET 1 BF 4 INVENTORS 3%; W; BY um PM /5. g ATTO [?N E Y PATENTED Jun 8 m2 SHEET 2 BF 4 Fig. 3

Fig. 2

PATENTEB JUU 8 1972 SHEET 3 BF 4 PATENIED JUL 1 8 I972 SHEET '4 UF 4 HYDRODYNAMIC REVERSING GEAR BACKGROUND OF THE INVENTION The invention relates to a hydrodynamic reversing gear, more particularly for railway locomotives and is of the type that has at least one pair of hydrodynamic work circuits with toroidal work chambers including bladed impeller and runner wheels. Each circuit of a pair is associated with a different direction of travel.

Gears of this type are installed mostly in locomotives intended for shunting or switching service which involves frequent reversals of the direction of travel and traction. This reversal can be achieved more easily, more rapidly and at long term, with greater reliability and with a smaller outlay for maintenance, in a completely hydraulic manner i.e. by filling and emptying corresponding Foettinger work circuits than by mechanical means such as jaw clutches. Locomotives which operate in large marshalling yards, and which are repeatedly required to attain high travelling speeds during service, also may profit from the completely hydraulic mode of reversal. They are therefore equipped with a total of four Foettinger convertors, two of which are used for starting and two for continuous travel in the forward and backward direction. The success of this principle-first in fairly small locomotives has resulted in the use for increasingly more powerful locomotives of similar, fully hydraulic, two-speed reversing gears equipped with a total of four convertors.

In gears of this type, the turbine wheels of the convertors intended for the opposite direction rotate oppositely to the pump wheels, which rotate in the same direction at all times. Although the convertors not in use are filled only with air, this medium, which possesses mass, causes relatively high losses due to the rotation in the opposite direction and due to the resulting intensive air turbulence. These losses reduce the overall efficiency of the reversing gear and cause, first of all, an increased fuel consumption. Where the power to be transmitted is relatively small, these losses are negligible and thus may be tolerated. In the case of larger gears, however, for which the ventilation or windage losses are also higher, difficulties have been encountered. Thus, the ventilation losses have caused a significant heating of the gear. Convertors with particularly high rotary speeds were primarily endangered. In the case of mechanical stepping of the gears this is the starting speed. By a purely hydraulic stepping of the two-speed reversing gear, an equal rotary speed is obtained on both the primary and secondary sides for both speeds, and this made possible to overcome the thermic difficulties in the required output range. Meanwhile, as a result of increases in the power of the gears, the utmost limit of tolerance has been reached with this method of reducing ventilation. Temperatures of 200 C. occur spotwise and oil nozzles become charred. Further increases of power are possible only if other appropriate measures are taken.

It has been suggested to construct the convertors with a double walled housing and to cool them with water. It has also been proposed to dimension the convertors very large for the purpose of reducing their rotary speed for a given power, and thus rendering the ventilation losses manageable. Both remedies are very expensive and require excessive space and weight. These are especially important factors particularly in the field of vehicles.

OBJECT, SUMMARY AND ADVANTAGES OF THE INVENTION It is an object of the invention to provide an improved reversing gear of the aforenoted type in which the generated heat is maintained under control even at very high power without greatly increasing cost, or adding to volume or weight.

Briefly stated, according to the invention, at least that pair of gear work circuits, in which the wheels attain the highest peripheral speed in service, is provided with flow obstructing members movable into the work chamber, and operable at will or automatically by control and/or actuating means. The flow obstructing members are moved into the work chamber associated with the work circuit after the latter has been emptied of hydraulic liquid, and are retracted only when the hydraulic liquid is readmitted to said work circuit.

By virtue of the flow obstructing members provided in the convertors and movable into the work chamber, or, more accurately, into the flow channels of the work chamber, circulation of the air in the liquid-free work chamber is eliminated or at least reduced to a negligible magnitude. In this manner, the blade wheels run in a stationary air environment and alternate acceleration and deceleration of the air in the blade rings no longer occur. The work performed by the blade rings and relating to this phenomenon has caused the air turbulence which resulted in the heating of the reversing gear components due to internal friction. According to the invention, the performance of such work is prevented by the flow obstructing members, since, as stated above, the air present between the blades is caused to be stagnant.

The invention will be better understood and further objects, as well as advantages will become more apparent from the ensuing detailed specification of several exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of a two-speed turbo reversing gear incorporating an embodiment of the invention;

FIG. 2 is an enlarged view of a detail of FIG. 1; FIG. 3 is a fragmentary view taken along line III-III of FIG.

FIG. 4 is an enlarged view of a detail of FIG. 2 identified by a dash-dot circle;

FIG. 5 is a view similar to that of FIG. 3 showing components in a different arrangement;

FIG. 6 is an axial sectional view of a convertor incorporating another embodiment of the invention;

FIG. 7 is a view similar to FIG. 6, depicting another embodiment of the invention;

FIG. 8 is a schematic sectional view taken along line VIII- VIH of FIG. 7;

FIG. 9 is a schematic view of a power means associated with the structure according to FIG. 7;

FIG. 10 is a view similar to FIG. 8 and depicts a modification of that embodiment;

FIG. 11 is a schematic sectional view taken along a plane normal to the convertor axis and illustrating still a further embodiment of the invention;

FIG. 12 is a fragmentary axial sectional view of a convertor incorporating the embodiment according to FIG. I 1;

FIG. 13 is a fragmentary axial sectional view of a convertor incorporating still another embodiment of the invention and FIG. 14 is a fragmentary sectional view along line XIV XIV of FIG. 13.

DESCRIPTION OF THE EMBODIMENTS Turning now to FIG. 1, the driving shaft 1 drives, through two spur gears 2 and 3, the central pump wheel shaft 4 on which there are keyed the pump wheels 5 and 8 of the two flow convertors I and II. The two turbine wheels 6 and 9 are rigidly connected to one another by means of a hollow shaft 11 carrying a spur gear 12. The central pump wheel shaft 4 is connected through two spur gears 13 and 14 to a second central pump wheel shaft 15 which carries, in addition to a spur gear 24 for the filling pump drive, the pump wheels 16 and 19 of the flow convertors III and IV. The respective turbine wheels 17 and 20 of the convertors IV and III are rigidly connected to one another by means of a hollow shaft 22 which is integral with a spur gear 23. The two spur gears 12 and 23 on the hollow turbine wheel shaft 11 and 22 mesh with the spur gear 25 mounted on the output shaft 26.

Since the two pump wheel shafts 4 and 15 are driven in opposite directions, but the two turbine wheel shafts l1 and 22 are connected in the same sense to the output shaft 26, the

two coaxial convertors l and II of the one group effect forward travel, and the two coaxial convertors III and IV of the other group effect backward travel. The convertors I and III are the low-speed or Starting convertors, while the convertors II and IV are the high-speed or cruising convertors. At any time only a single convertor is filled with hydraulic liquid to thus transmit an output torque.

In the emptied convertors associated with the opposite travel direction, the pumps and the turbine wheels rotate in mutually opposite directions. The strongly turbulent air masses in the air-filled convertor work chamber would cause a substantial loss of efliciency and heating which may become destructive with increasing size of the convertor, unless countermeasures are adopted.

Thus, according to a first embodiment of the invention, the convertors are provided with flow obstructing means formed of elastic flaps 29 movable in and out of an operative position in the work chamber. These flaps 29 are shown in profile in FIGS. 1-5.

FIG. 2 illustrates the use of the flow obstructing elastic flaps 29 in a hydrodynamic convertor having a pump wheel 30 exposed to a throughgoing centrifugal flow, a radially outwardly adjacent turbine wheel 31 and a guide blade ring 32 exposed to a throughgoing centripetal flow. The hydraulic liquid which, when working, circulates meridionally, is guided within the blade rings and in the bladeless spaces by an outer and an inner core ring wall; more particularly, the guide wheel cover disc 33 is drawn well forward at the inlet and outlet and forms a major wall section of the core ring.

A wall section located radially outwardly of the cover disc 33 is axially oriented and merges with a large radius into a radial wall section, which is the guide wheel cover disc proper (FIG. 4). At the axial location, thin steel plates 29 are secured to the outer face of the aforenoted wall section in front of the entry into the fin channels by electric spot welds 28. When the convertor is empty, i.e. void of hydraulic fluid, these plates 29 project axially as far as the opposite housing wall and prevent the air, thrown outwardly by the rotating pump wheel, from passing through the guide wheel. The air strikes the plates of flaps 29 projecting into the meridional cross section of the toroidal work chamber and is thus halted in its flow. Due to the stagnation of the air, the otherwise usual air circulation within the work chamber does not occur and consequently no energy is consumed therefor.

If hydraulic fluid, which generally has a specific gravity about 700-750 times greater than air, is introduced into the work chamber of the running convertor, the dynamic pressure (pressure head) exerted upon flaps 29 projecting freely into the chamber due to the increase in the specific gravity. As a result, even at low primary speeds or only partial filling, the resilient flaps yield to the liquid flow and conform closely to a wall portion of the work chamber. Thus, in this condition, the flaps 29 do not affect the characteristics of the work circuit.

In order to ensure that the flaps 29, when in a deflected position (i.e. when they lie flat against a wall face in the work chamber), are not exposed to excessive stresses which might tear them loose, those areas of the cover disc 33 which are contacted by the deflected flaps 29 should preferably be smooth and curved only unidimensionally. Such areas are indicated in FIGS. 3 and 4 with dashed lines which also designate the inoperative (i.e. flow transmitting) deflected position of flaps 29.

FIG. 5 shows how the unidimensional curvature and the smooth surface of the blades themselves are utilized as a contact area for the flaps 29. In this figure, straight rectangular spring steel plates are electrically spot welded along one side, similarly as shown in FIG. 4, to the rounded head portion of the blades so that the flaps extend tangentially from the rounded head portion and abut against the surface of the opposite blade across the blade channel. Thus, the latter is blocked by the extended flaps. When work fluid flows through the guide wheel, the flaps are deflected out of the blade channel in the flow direction and rest smoothly against the associated blades.

The aforedescribed structure constitutes a particularly simple embodiment of the invention, since no separate actuating means are required. Thus, there is virtually no additional weight and the structural outlay is increased only to a very small degree.

Turning now to the embodiment shown in FIG. 6, there is illustrated a convertor having a pump wheel, a turbine wheel, a first guide wheel 43 and a second guide wheel 44. In this structure the flow obstructing means is formed of a cylindrical sleeve 45 surrounding the convertor axis and slidably guided in the convertor housing. The sleeve 45 is held by a plurality of small hydraulic power assemblies disposed in a circular array in the convertor housing about the convertor axis. Each power assembly comprises a hydraulic cylinder 46 and a piston 49 reciprocable therein. Each piston 49 is rigidly secured to the cylindrical sleeve 45. In each cylinder 46 there is disposed a spring 47 urging piston 49 into a position in which the sleeve 45 is substantially withdrawn from the work chamber of the convertor. Each hydraulic cylinder is connected in parallel with the pressure chamber of the filling and voiding (emptying valve 48, 50 associated with the convertor.

Thus, when the work chamber of the convertor is voided of hydraulic liquid, a hydraulic pressure is automatically applied to each piston 49. Since the force derived from this hydraulic pressure is greater than and opposite to the force of spring 47, the pistons 49 move against the force of springs 47 and thus advance the cylindrical sleeve 45 into the convertor work chamber into its operative position depicted in FIG. 6. On the other hand, when the work chamber of the convertor is filled with hydraulic liquid through valve 48, 50, the pressurized hydraulic liquid is drained from each cylinder 46. As a result, springs 47 cause a withdrawal of cylindrical sleeve 45 from the convertor work chamber into an inoperative position. Since the flow obstructing sleeve 45 is never exposed to the force of the hydraulic work liquid in the convertor, it may be of light and inexpensive structure.

In the embodiment according to FIGS. 79, the air flow obstructing means are formed by a rotary plug-like structure constituted by the guide wheel itself. Along a dividing circle 51 concentric with the center of rotation of the convertor, the blades of the guide wheel 52 are divided into a head part 53 and a tail part 54. The tail parts 54 of the guide wheel blades are afi'lxed to the convertor housing. The head parts 53 are combined in a guide blade head ring 55 which is movable with respect to the blade tails in the peripheral direction by at least half a blade pitch. For this purpose, a pin 56 is passed through the guide wheel housing through a slot 60 extending in the peripheral direction. Externally of the guide wheel housing there is provided a hydraulic power assembly formed of a cylinder 58 attached to the guide wheel housing at 59, a piston 58" reciprocably held therein, and a piston rod 57 attached to piston 58" at one end and to pin 56 at the other end. The piston 58" may be displaced by a spring 58 disposed in cylinder 58 into a terminal position of rest, setting the guide wheel structure into an air flow blocking position. By applying pressure through conduit 61, to the piston 58", the latter is displaced into another end position in which the air flow obstructing structure of the guide wheel opens so that the latter may perform its normal function associated with the flow of hydraulic liquid. In FIG. 8 the head parts 53 are shown in a staggered position with respect to the tail parts 54. In this position, the head parts, which form the flow obstructing means according to the invention, are in their operative (air flow blocking) position. At the same time, the actuating means for the head parts 53 is in a position shown in FIG. 9. In their inoperative (non-blocking) position, the head parts 53 are aligned with associated tail parts. This is achieved by a rotary motion of small angle of the head parts 53 about the convertor axis, caused by the piston assembly 57, 58" which moves, upon pressurization of conduit 61, the pin 56 to an opposite end of slot 60.

Since the conduit 61 is in communication with the work chamber of the convertor, it is pressurized only when the convertor is filled with hydraulic liquid. Thus, the operation of the flow obstructing means is automatic.

In a manner similar to the embodiment according to FIGs. 7-9, blade sections from the central part of the blade-divided along concentric dividing lines and combined into pivotable rings-may be slid out of the blade into the adjacent blade channel cross section. If the blade channel is wider in the peripheral direction than the maximum blade thickness, two adjoining movable central blade sections are provided which are mutually independent and pivotable into the adjacent blade channel in the manner illustrated in FIG. 10.

Turning now to the embodiment illustrated in FIGS. 11 and 12, the guide wheel blades are identified at 62. Every other blade 62 is pivotally held in an eccentric manner by pin 63 passing through the guide wheel housing. As well seen in FIG. 11, when the pivotable blades 62 are inclined with respect to the non-pivotable blades (position shown in solid lines), the blade channels are blocked. In this position the pivotable blades 62 function as air flow obstructing members. If, on the other hand, the last-named blades assume a position shown in dotted lines, no obstruction to flow exists.

For setting the pivotable blades into an operative (flow blocking) or inoperative (flow transmitting) position, there is provided a hydraulic motor 64 adapted to turn ring gear 65 arranged coaxially with the convertor axis. Externally of the guide wheel housing, to each pin 63 there is aflixed a segment gear 66 which meshes with the ring gear 65. It is apparent that dependent upon the energization of motor 64, the pivotable blades 62 are swung into one or the other position.

Turning now to FIGS. 13 and 14, the flow obstructing structure shown therein is similar to the embodiment illustrated in FIGS. 1-5 insofar as no separate actuating means are needed to move the flow obstructing members into their operative or inoperative positions.

The flow obstructing members according to the embodiment shown in FIGS. 13 and 14 are formed of rigid flaps 70 hingedly secured in the zone of the blade head of the guide blades 71 inside of the converter. For this purpose, with each flap 70 there is associated a hinge pin 72 which passes axially parallel through the converter housing and is held rotatably in the housing wall 73 and in the core ring wall 74. Each flap surrounds its associated hinge pin 72 closely with a sleeve-like bent end which-turned inward at an acute angleextends in an axial groove of the hinge pin. In this manner it is ensured that the flap 70 and hinge pin 72 will rotate as a unit. At the terminus of the hinge pin 72 that projects into the inside of the core ring there is provided a slot into which fits the inner central end of a spiral spring 75. The other, outer end of each spiral spring is secured to the ring wall 74 at locations 76. The direction of winding of the spiral spring and the circumferential position of the location 76 are, with respect to the pivotal axis of the hinge pin 72, chosen in such a manner that the spring exerts on the hinge pin a clockwise torque when viewed in FIG. 14. This torque, in turn, tends to rotate the flap 70 in an arc indicated with broken lines in FIG. 14. The flow of hydraulic liquid illustrated by the three substantially parallel arrows in FIG. 14, exerts a force to each flap 70 against the force of the springs 75 and swings the flaps against the back side of each associated blade where it fits into a recess which is provided in the blades 71 and which corresponds to the thickness of the flap. In this manner, the flaps are completely withdrawn and do not obstruct the flow of the hydraulic liquid. This condition is illustrated in FIG. 14. When the concertor is voided of hydraulic liquid, the flaps 70 automatically swing out into their operative position urged by the springs 75 and thus effectively prevent the circulation of air in the convertor.

The advantages of the invention reside in the act that by simple means which have no adverse effect upon the efficiency of the individual convertor, the efficiency of the entire reversing gear is increased since the losses of the empty convertors which rotate in mutually opposite direction on the primary and secondary sides are eliminated. Furthermore, due to the elimination of the windage losses according to the invention, the fully hydraulic reversing gears may be designed for heavier duty which they are capable to perform without inadmissible heating.

What is claimed is:

1. In a hydrodynamic reversing gear particularly for railtype vehicles, said reversing gear being of the type that includes (A) at least one pair of hydrodynamic work circuits, one circuit of each pair being operational for one direction of travel, the other circuit of each pair being operational for the other, opposite direction of travel; each circuit includes a work chamber formed of a circular array of blades of an impeller wheel and a circular array of blades of at least a runner wheel, and (B) means for introducing hydraulic liquid into said work circuits to render them selectively operational and withdrawing hydraulic liquid from said work circuits to render them selectively inoperational, the improvement comprising A. flow obstructing means formed of a plurality of flaps secured in said work chamber, said flow obstructing means being associated with at least one of said circuits and movable into an operative or flow blocking position in the work chamber of said last named circuit and into an inoperative or flow transmitting position and B. resilient means associated with each flap for urging the latter into said flow blocking position; the force of said resilient means being so designed that each flap yields to the flow of hydraulic liquid in the work circuit and moves into the flow transmitting position and each flap, when the work circuit is void of hydraulic liquid, withstands the flow of air in said work circuit and remains in said flow blocking position.

2. In a hydrodynamic reversing gear particularly for railtype vehicles, said reversing gear being of the type that includes (A) at least one pair of hydrodynamic work circuits, one circuit of each pair being operational for one direction of travel, the other circuit of each pair being operational for the other, opposite direction of travel; each circuit includes a work chamber formed of a circular array of blades of an impeller wheel and a circular array of blades of at least a runner wheel, and (B) means for introducing hydraulic liquid into said work circuits to render them selectively operational and withdrawing hydraulic liquid from said work circuits to render them selectively inoperational, the improvement comprising A. flow obstructing means formed of at east one portion of at last some of the blades associated with a wheel, said flow obstructing means being associated with at least one of said circuits and movable into an operative or flow blocking position in the work chamber of said last-named circuit and into an inoperative or flow transmitting position, each blade of the wheel containing said flow obstructing means being divided along at least one dividing circle into at least two portions movable with respect to one another in a circumferential direction to an extent equalling approximately one-half the distance between two adjacent blades and B. actuating means for moving said flow obstructing means into the flow blocking position when said work chamber is voided of hydraulic liquid and into the flow transmitting position upon introducing hydraulic liquid into said work circuit.

3. In a hydrodynamic reversing gear particularly for railtype vehicles, said reversing gear being of the type that includes (A) at least one pair of hydrodynamic work circuits, one circuit of each pair being operational for one direction of travel, the other circuit of each pair being operational for the other, opposite direction of travel; each circuit includes a work chamber formed of a circular array of blades of an impeller wheel and a circular array of blades of at least a runner wheel, and (B) means for introducing hydraulic liquid into said work circuits to render them selectively operational and withdrawing hydraulic liquid from said work circuits to render them selectively inoperational, the improvement comprising A. flow obstructing means formed of at least some of the blades associated with a wheel, said flow obstructing means being associated with at least one of said circuits and movable into an operative or flow blocking position in the work chamber of sad last-named circuit and into an inoperative or flow transmitting position, each blade forming said flow obstructing means being pivotable in the circumferential direction and abutting, in its flow blocking position, two immediately adjacent blades in said wheel and B. actuating means for moving said flow obstructing means into the flow blocking position when said work chamber is voided of hydraulic liquid and into the flow transmitting position upon introducing hydraulic liquid into said work circuit.

4. In a hydrodynamic reversing gear particularly for railtype vehicles, said reversing gear being of the type that includes (A) at least one pair of hydrodynamic work circuits, one circuit of each pair being operational for one direction of travel, the other circuit of each pair being operational for the other, opposite direction of travel; each circuit includes a work chamber formed of a circular array of blades of an impeller wheel and a circular array of blades of at least a runner wheel, and (B) means for introducing hydraulic liquid into said work circuits to render them selectively operational and withdrawing hydraulic liquid from said work circuits to render them selectively inoperational, the improvement comprising A. flow obstructing means formed of a cylindrical sleeve axially slidably held coaxially with said wheels, said flow obstructing means being associated with at least one of said circuits and movable into an operative or flow blocking position in the work chamber of said last-named circuit and into an inoperative or flow transmitting position and B. actuating means for moving said flow obstructing means into the flow blocking position when said work chamber is voided of hydraulic liquid and into the flow transmitting position upon introducing hydraulic liquid into said work circuit, said actuating means including 1. spring means urging said cylindrical sleeve into one of said positions, 2. power means overcoming, when energized, the force of said spring means to move said cylindrical sleeve into the other of said positions and 3. means for energizing and de-energizing said power means simultaneously with the introduction of hydra ulic liquid into and the withdrawal of hydraulic liquid from the work circuit.

5. An improvement as defined in claim 1, wherein each flap is made of a resilient material, the resiliency of which constitutes said resilient means.

6. An improvement as defined in claim 1, including a spring connected to each flap and constituting said resilient means, said improvement further includes abutment means associated with each flap to arrest it in said flow transmitting position.

7. An improvement as defined in claim 1, wherein said flaps are secured to the guide wheel at the inlet side thereof and extend in their flow blocking position across flow channels defined by the blades of the guide wheel.

8. An improvement as defined in claim 2, wherein said dividing circle passes through the thickest portions of said blades measured in the circumferential direction.

9. An improvement as defined in claim 2, wherein said actuating means includes A. spring means urging said portions constituting said flow obstructing means into said flow blocking position and B. means operatively connected with said means for introducing hydraulic liquid into and withdrawing the same from the work circuit, for moving said flow obstructing means into said flow transmitting position against the force of said spring means automatically when hydraulic liquid is introduced into the work circuit, and allowing said flow obstructing means to move into said flow blocking position under the force of said spring means automatically when hydraulic liquid is withdrawn from said work circuit. 

2. power means overcoming, when energized, the force of said spring means to move said cylindrical sleeve into the other of said positions and
 2. In a hydrodynamic reversing gear particularly for rail-type vehicles, said reversing gear being of the type that includes (A) at least one pair of hydrodynamic work circuits, one circuit of each pair being operatiOnal for one direction of travel, the other circuit of each pair being operational for the other, opposite direction of travel; each circuit includes a work chamber formed of a circular array of blades of an impeller wheel and a circular array of blades of at least a runner wheel, and (B) means for introducing hydraulic liquid into said work circuits to render them selectively operational and withdrawing hydraulic liquid from said work circuits to render them selectively inoperational, the improvement comprising A. flow obstructing means formed of at east one portion of at last some of the blades associated with a wheel, said flow obstructing means being associated with at least one of said circuits and movable into an operative or flow blocking position in the work chamber of said last-named circuit and into an inoperative or flow transmitting position, each blade of the wheel containing said flow obstructing means being divided along at least one dividing circle into at least two portions movable with respect to one another in a circumferential direction to an extent equalling approximately one-half the distance between two adjacent blades and B. actuating means for moving said flow obstructing means into the flow blocking position when said work chamber is voided of hydraulic liquid and into the flow transmitting position upon introducing hydraulic liquid into said work circuit.
 3. In a hydrodynamic reversing gear particularly for rail-type vehicles, said reversing gear being of the type that includes (A) at least one pair of hydrodynamic work circuits, one circuit of each pair being operational for one direction of travel, the other circuit of each pair being operational for the other, opposite direction of travel; each circuit includes a work chamber formed of a circular array of blades of an impeller wheel and a circular array of blades of at least a runner wheel, and (B) means for introducing hydraulic liquid into said work circuits to render them selectively operational and withdrawing hydraulic liquid from said work circuits to render them selectively inoperational, the improvement comprising A. flow obstructing means formed of at least some of the blades associated with a wheel, said flow obstructing means being associated with at least one of said circuits and movable into an operative or flow blocking position in the work chamber of sad last-named circuit and into an inoperative or flow transmitting position, each blade forming said flow obstructing means being pivotable in the circumferential direction and abutting, in its flow blocking position, two immediately adjacent blades in said wheel and B. actuating means for moving said flow obstructing means into the flow blocking position when said work chamber is voided of hydraulic liquid and into the flow transmitting position upon introducing hydraulic liquid into said work circuit.
 3. means for energizing and de-energizing said power means simultaneously with the introduction of hydraulic liquid into and the withdrawal of hydraulic liquid from the work circuit.
 4. In a hydrodynamic reversing gear particularly for rail-type vehicles, said reversing gear being of the type that includes (A) at least one pair of hydrodynamic work circuits, one circuit of each pair being operational for one direction of travel, the other circuit of each pair being operational for the other, opposite direction of travel; each circuit includes a work chamber formed of a circular array of blades of an impeller wheel and a circular array of blades of at least a runner wheel, and (B) means for introducing hydraulic liquid into said work circuits to render them selectively operational and withdrawing hydraulic liquid from said work circuits to render them selectively inoperational, the improvement comprising A. flow obstructing means formed of a cylindrical sleeve axially slidably held coaxially with said wheels, said flow obstructing means being associated with at least one of said circuits and movable into an operative or flow blocking position in the work chamber of said last-named circuit and into an inoperative or flow transmitting position and B. actuating means for moving saiD flow obstructing means into the flow blocking position when said work chamber is voided of hydraulic liquid and into the flow transmitting position upon introducing hydraulic liquid into said work circuit, said actuating means including
 5. An improvement as defined in claim 1, wherein each flap is made of a resilient material, the resiliency of which constitutes said resilient means.
 6. An improvement as defined in claim 1, including a spring connected to each flap and constituting said resilient means, said improvement further includes abutment means associated with each flap to arrest it in said flow transmitting position.
 7. An improvement as defined in claim 1, wherein said flaps are secured to the guide wheel at the inlet side thereof and extend in their flow blocking position across flow channels defined by the blades of the guide wheel.
 8. An improvement as defined in claim 2, wherein said dividing circle passes through the thickest portions of said blades measured in the circumferential direction.
 9. An improvement as defined in claim 2, wherein said actuating means includes A. spring means urging said portions constituting said flow obstructing means into said flow blocking position and B. means operatively connected with said means for introducing hydraulic liquid into and withdrawing the same from the work circuit, for moving said flow obstructing means into said flow transmitting position against the force of said spring means automatically when hydraulic liquid is introduced into the work circuit, and allowing said flow obstructing means to move into said flow blocking position under the force of said spring means automatically when hydraulic liquid is withdrawn from said work circuit. 